In general, a syringe is an instrument for injecting a liquid medicine into a body of an animal/plant and is configured to pierce a skin with a sharp tip thereof to allow the liquid medicine to be injected into any tissue of the body.
FIG. 1 is an exploded perspective view illustrating a conventional syringe. As shown in FIG. 1, the syringe generally includes a cylinder 20 to which an injection needle 10 is coupled and in which an injection liquid is contained, and a plunger 30 provided in the cylinder 20 so as to be movable forward and backward.
In this conventional syringe, as the plunger 30 is moved backward, a negative pressure is generated in the cylinder 20 and the cylinder is then filled with an injection liquid. As the plunger is moved forward, the injection liquid in the cylinder 20 is discharged through the injection needle 10 by a positive pressure and then injected into a patient's body.
However, when this conventional syringe is used, there is concern that foreign substances incorporated in the injection liquid itself or foreign substances such as glass particles scattered into and mixed with the injection liquid during a process of breaking and opening an ampoule in which the injection liquid is stored may be injected together with the injection liquid into the patient's body.
To solve this problem, a filtering syringe provided with a filter for filtering foreign substances contained in an injection liquid has been developed.
First, as disclosed in Korean Patent Laid-Open Publication No. 2012-87587, a conventional filtering syringe in which a filter for filtering foreign substances is provided in an injection needle or a cylinder performs a function of filtering foreign substances from an injection liquid sucked into the cylinder.
However, since foreign substances had been stuck to an outer surface of the injection needle introduced into an ampoule when the injection liquid is sucked, or foreign substances incorporated in the injection liquid remaining within the injection needle had not been filtered, it was impossible to fundamentally prevent the foreign substances from being injected together with the injection liquid into a patient's body.
In response thereto, U.S. Pat. No. 4,180,071 discloses an example in which a filter for filtering foreign substances is provided in a cap for covering an injection needle.
FIG. 2 is an exploded perspective view illustrating a conventional filter-cap syringe, and FIG. 3 is a sectional view illustrating a main portion of the conventional filter-cap syringe, wherein FIGS. 2 and 3 illustrate the conventional filter-cap syringe disclosed in U.S. Pat. No. 4,180,071.
Since the conventional filter-cap syringe has a cap 40 provided with a filter 41 as shown in FIG. 3 so that foreign substances are filtered by the filter 41 when an injection liquid is sucked, and the cap 40 including the filter 41 is detached from an injection needle 10 upon injection of the injection liquid, there is no concern that foreign substances may be injected.
However, in the conventional filter-cap syringe, the filter cap should have a diameter smaller than that of an inlet of a vial. If the diameter of the filter cap is larger, it is difficult to form a sharp tip having high strength and thus there is a limitation on increase in the area of the filter means.
In addition, the conventional filter-cap syringe has a technical problem in that since the injection liquid may be sucked into a cylinder 20 only via the minute injection needle 10 after passing through the filter 41 provided in the cap 40, a relatively large force is required for sucking the injection liquid and thus it is very inconvenient to use the syringe.